Lecture 7: Drug Development I

Comparison of Small Molecule and Biological Drugs

• Small Molecule Drugs

  • Characterized by low molecular weight.

  • Produced through chemical synthesis.

  • Features a well-defined structure.

• Biological Molecules (Biopharmaceuticals)

  • Characterized by high molecular weight.

  • Derived from living organisms.

  • Possess large and complex structures.

  • Examples include peptides (such as insulin), enzymes, and monoclonal antibodies.

• Monoclonal Antibodies (Specific Attributes)

  • High molecular weight.

  • High degree of complexity.

  • Development involves new processes and is typically handled on a case-by-case basis.

  • Development tends to be slower and more expensive compared to small molecules.

Growing Trends in Biologics

• Biologics have accounted for more than one-third of all new medicine approvals over the past decade.

• There is a significant growing trend for more biologics-based therapies, with a specific focus on monoclonal antibodies.

• Key Categories and Examples:

  • Antibody-based therapies: anti-VEGF and anti-PD-L1.

  • Vaccines: Human papilloma virus (HPV) and Covid-19.

  • RNA interference (RNAi): Duchenne Muscular Dystrophy (DMD).

  • Cell-based therapies: CAR-T for children with acute lymphoblastic leukemia.

  • Gene therapy: Adeno-associated virus (AAV) delivery of Factor IX as a therapy for haemophilia.

Animal Toxicology and Safety Assessment

• Preclinical Requirements:

  • The selection of a relevant animal model is critical.

  • A surrogate molecule may be used as an alternative.

  • Off-target toxicology is considered uncommon for biopharmaceuticals.

• Adverse Reactions:

  • Exaggerated pharmacology related to the intended mechanism.

  • Anti-drug antibody (ADA) responses: These can result in accelerated clearance of the drug, prolongation of exposure, or neutralization of pharmacological activity.

• Toxicity Assessment Guidelines:

  • When assessing toxicity for a human protein, the maximum dose is typically established at $10 \times$ the maximum exposure observed in the clinic.

• Immunotoxicology Comparisons:

  • Small molecules: Often exhibit unexpected and off-target effects.

  • Biopharmaceuticals: Require a thorough understanding to anticipate risks such as infusion reactions and cytokine storms.

  • Risk anticipation for cytokine release may involve NHP (Non-Human Primate) blood cell cytokine release assays.

  • Phase I Dosing: The initial dose in Phase I trials is based on the minimum anticipated biological effect.

Phase I Clinical Trial Objectives and the TGN1412 Case Study

• Phase I Objectives:

  • Determining if the drug is safe.

  • Evaluating how well the drug is tolerated.

  • Identifying pharmacokinetic properties.

  • Investigating whether it is ethical or possible to test the drug in healthy volunteers.

• TGN1412 (CD28-SuperMAB) Case Study:

  • The drug had a very good preclinical profile.

  • The human dose administered was 500 times lower than doses used in preclinical testing.

  • Despite the low dose, six volunteers were hospitalized with cytokine release syndrome.

Immunotherapy Principles and Key Mechanisms

• Definition: A form of cancer treatment that utilizes the immune system to attack cancer cells, similar to the way it targets bacteria or viruses.

• Checkpoint Inhibitors:

  • These work by releasing a natural "brake" on the immune system.

  • This allows T cells to recognize and attack tumors.

• CAR T Cell Therapy:

  • Chimeric antigen receptor (CAR) T cell therapy involve genetically engineering a patient’s own immune cells.

  • The cells are modified to produce a new protein, turning them into "supercharged" cancer fighters.

• PD-1 and PD-L1 Interaction:

  • The PD1 receptor is located on the T-Cell.

  • The PD-L1 antigen is located on the Tumour Cell.

  • PD1 tamps down the immune system.

  • PD-L1 protects cancers from T-cells.

  • Antibodies are used to block these interactions, allowing T-cells to engage the tumor cell.

Historical Milestones in Immunotherapy

• 1976: Interleukin 2 was introduced, though it was associated with many serious adverse events.

• 1990: James Allison (Berkeley) identified Cytotoxic T-lymphocyte-associated protein 4 (CTLA-4) on the T-cell surface. Blocking CTLA-4 caused tumors to vanish.

• 1999: Tasuku Honjo (University of Kyoto) identified Programmed Cell Death Protein 1 (PD1) and Programmed death-ligand 1 (PD-L1).

Pembrolizumab (Keytruda) Development and Efficacy

• Development History:

  • 2006: Invented at Organon.

  • 2007: Schering-Plough acquired Organon.

  • 2009: Acquired by Merck (initially with little interest).

  • 2011: Phase 1 trial led to Breakthrough Therapy Designation and expansion to 1300 patients.

• Performance Characteristics:

  • Efficacy varies: it may not work at all for some, while for others, it can eliminate cancer, stabilize it, or cause regression.

  • Responses are often long-lasting.

  • Response Rates by Cancer Type:

    • Hodgkin's Lymphoma: $90\%$

    • Pancreatic and Colorectal Cancer: $0\%$

  • The drug shifted the research landscape, leading to over 1000 clinical trials.

CAR-T Therapy Evolution and Approved Treatments

• Limitations of Early CAR-T:

  • Primarily targeted CD19, which is common only to certain blood cancers.

  • Potential for fatal immune reactions.

• Emily Whitehead Case:

  • Diagnosed with leukemia in 2010.

  • Became the first pediatric patient to receive CAR-T therapy in 2012, a pioneering moment in immune reprogramming.

• Applications Beyond Cancer: Potential use in asthma, autoimmune diseases (lupus, multiple sclerosis), fibrosis, aging-related conditions, and infectious diseases (virus-specific T cells).

• Approved Therapies Table:

Challenges in Cell Therapy: Cost and Scalability

• Economic Barriers:

  • Treatments cost between $300,000$ and $6,000,000$ USD.

  • There is limited insurance coverage for these therapies.

• Efforts to Reduce Costs:

  • Utilizing larger reaction vessels for production efficiency.

  • Reducing labor and material costs.

  • India's ImmunoACT has produced the first "cut-price" CAR-T at $40,000$, though this remains inaccessible for many.

• The Allogeneic Solution:

  • Moving toward "off-the-shelf" products using allogeneic cells to solve manufacturing bottlenecks.

  • The goal is a "Henry Ford moment" where engineered immune cells are mass-produced.

Biological Challenges and Rejection Mechanisms

1. T cell-mediated rejection: The host’s T cells recognize allogeneic cell surface markers (HLA mismatches) and mount a cytotoxic response.

2. Natural Killer (NK) cell activation: NK cells eliminate cells that lack self-MHC molecules.

3. Innate immune activation: An inflammatory environment created by cytokines enhances rejection.

4. Graft vs Host Rejection: The graft may impact tissues beyond the target and destroy joints or organs.

Engineering Strategies for Universal Donor Cells

• HLA Engineering: Knocking out HLA class I and II molecules to prevent host T cell recognition. Overexpressing HLA-E or HLA-G to protect against NK-mediated killing.

• Immune Checkpoint Modulation: Removing checkpoints like PD-1 to rewrite engagement rules.

• Virus-Specific T Cells (VSTs): Using VSTs for CAR-T therapy to ensure longer persistence due to stimulation from latent viral antigens, preventing exhaustion.

• Universal Donor Cells: Engineered with multiple layers of immune evasion circuits to make them "invisible" to the immune system.

• Specific Modifications and Optimization Targets:

  • Prevention of Exhaustion: Targeting LAG3, FAS, and PD1.

  • Host vs Graft Rejection: Targeting B2M and CD52.

  • Fratricide Resistance: Targeting CD7, CD5, CD2, and TRAC.

  • Persistence/Infiltration: Engineering cytokine receptors (IL15, IL21) and addressing the Tumor Microenvironment (A2AR, TGF-B, Selectins).

  • CAR Optimization: Focusing on CD3Z, 41BB, and CD8$\alpha$.

Current Clinical State and Future Directions

• Clinical Trial Statistics (as of 5 March 2025):

  • Total Cell Therapy trials: 2707.

  • Completed: 599.

  • Recruiting: 797.

  • Completed Allogeneic trials: 50.

  • Allogeneic recruiting: 54.

  • Not yet recruiting (Allogeneic): 26.

• Future Vision:

  • Cell therapies without time-consuming or costly hurdles.

  • Immune rejection becomes a problem of the past.

  • Transition from a privilege to a standard of care.

  • "Off-the-shelf" treatments that are instant, effective, and universally accessible.